What should you know about complications of dehydration?

When the body loses more fluid than it replaces, blood volume can fall and the kidneys may conserve water by making less concentrated urine. Dehydration may follow vomiting, diarrhoea, fever, heavy sweating, heat exposure, or difficulty drinking. Dark urine, dry mouth, thirst, headache, dizziness, and constipation can be clues, although symptoms vary.

More severe dehydration can reduce blood flow to the brain and kidneys. It may cause weakness, fast breathing, fainting, confusion, or very little urine. Electrolyte changes can affect muscles and the heart, particularly when fluid losses are continuing or replacement is unsuitable.

Start small, frequent sips of water or an oral rehydration solution if the person can drink. After vomiting, pause briefly and try again with smaller amounts. Continue suitable food when tolerated, and address the cause, such as gastroenteritis or heat exposure. Avoid relying on alcohol, and ask a clinician about fluid limits if heart or kidney disease is present.

Watch urine output, alertness, thirst, and ability to keep fluids down. A clinician may need to assess the person, review medicines, check electrolytes, or give fluids through a vein when oral replacement is not enough.

Seek urgent help for confusion, fainting, severe weakness, inability to drink, repeated vomiting, very little urine, cold or clammy skin, or breathing difficulty. Get prompt assessment after heat exposure if the person is confused or not improving with cooling and fluids. Children, older adults, and people with chronic illness may need earlier review when losses continue.

Ask what caused the fluid loss, which drinks or rehydration solution are suitable, whether medicines need adjustment, and how to monitor urine and alertness. Confirm the warning signs for your age and health conditions, and ask when blood tests or supervised fluid treatment are needed.